Digital communications systems often include one or more of a lock detector, a modulation classifier, and an SNR estimator. A lock detector is used, for example, when a receiver is coherently demodulating a carrier that it has received to determine whether a local carrier used for demodulation is in phase with the received carrier. A modulation classifier is used, for example, to determine which modulation scheme has been used to modulate the received carrier. Exemplary modulation schemes include various types of phase shift keying such as binary phase shift keying, quaternary phase shift keying, and more generally M-ary phase shift keying where M is theoretically any positive integer. An SNR estimator is used, for example, to estimate the SNR of the symbols transmitted using the received carrier.
In digital communications, and particularly in mobile digital communications, it is beneficial to employ circuitry that is fast, inexpensive, relatively simple, and power efficient. Accordingly, research and development continue into improving the designs of lock detectors, SNR estimators, and modulation classifiers.